The present invention relates to a crop cutting device comprising:
a frame structure arranged for forward travel over ground having a standing crop thereon;
a cutter bar secured to the frame structure and extending transversely across a front end of said frame structure;
a plurality of knife guards mounted in spaced relation along said cutter bar and projecting forwardly therefrom in transverse alignment;
each of said guards having an upwardly facing ledger surface with opposed side edges thereof arranged to provide first and second shearing edges;
at least one sickle bar;
the sickle bar being mounted in transversely extending position and being driven for reciprocating movement relative to said knife guards;
the sickle bar having a plurality of knife blades mounted thereon for movement therewith;
each of the knife blades having a bottom cutting surface for passing across the upwardly facing ledger surface of the knife guards in a shearing action and a top opposed surface;
each of the knife blades having two side cutting edges which are chamfered from the top opposed surface down to the cutting surface to cooperate with the shearing edges of said knife guards;
each of the first and second sickle bars being driven by a distance substantially equal to the distance between two knife guards such that each knife blade moves from a position at the outboard end of each stroke generally aligned with one of the knife guards to a position at the inboard end of each stroke generally aligned with a next adjacent knife guard.
The term “sickle bar” as used herein is intended to refer generally to a structure which supports all of the knife blades at the spaced positions along its length and is not intended to be limited to a single continuous element extending along the whole length of the structure. Thus the bar may be formed of different elements at different parts of the length and may include pieces below and above the blades.
It is well known that many sickle knives of this general type include a conventional or pointed guard where the guard is formed as an integral element which includes a base piece attached to the cutter bar and defining the ledger surface and a nose piece projecting forwardly from the ledger surface in front of the front edge of the blade which is generally pointed at a leading end so as to separate the crop to each side of the guard. This nose piece also stands up in front of the ledger surface to protect the front edge of the blade and includes a rearwardly extending shelf over the ledger surface which forms a slot with the ledger surface through which the blade passes. Guards of this type include separate hold down members between the guards which apply downward pressure on the cutter bar to press the blades against the ledger surface.
Pointed guards generally feature a point with a cut slot that the sickles sections reciprocate in and out of. Various types of hold-down arrangement are used to apply pressure to the sickle to keep its shearing surface in close contact with the guard ledger as cutting occurs. Usually these are located between the guard point or at the rear edge of the sickles. Most are sheet metal and feature easy adjustment using a hammer or a simple single point threaded adjustment. By keeping the hold-downs separate from the guards fewer hold-downs than points may be used to reduce the cost and number of adjustments required. Pointed guards have found much favour in easier cutting conditions due to the ease of adjustment and superior performance.
Another form of guard is known as a stub guard which is formed in two separate pieces including a base piece which carries the ledger surface and a top piece which extends over the ledger surface. The pieces are separate and separately adjustable relative to the cutter bar so that the top piece can apply pressure onto the blade to press it onto the ledger surface. The pieces terminate at a front edge which is just behind the front edge of the blade so that the front edge of the blade is presented to the crop. As this front edge must have a significant width for strength, there is a risk that crop engages this front edge rather than the side cutting edges of the blade.
In tough cutting, stub or no-clog guards have found the most favour. Stub guards use a separate top and bottom guard pieces that spaced slightly more than one sickle thickness apart create a slot for the sickle to operate in. The front edge of the sickle section protrudes slightly past the front tip of the two guard sections. This feature is what originally gave stub-guards their non-clogging self-cleaning action. A major improvement in stub guard technology was made when fully adjustable top hold-down assemblies were introduced as shown in U.S. Pat. No. 4,894,979 (Lohrentz) issued Jan. 23, 1990 and in U.S. Pat. No. 4,909,026 (Molzahn) issued Mar. 20, 1990. These arrangements allowed the gap to be controlled much more precisely than previously so that the shearing surface of the blade was kept in close contact with the guard ledger surface. This adjustability allows the stub top to act as a much more effective hold-down than the hold-downs found on regular pointed guard systems.
One drawback of the stub guard system is that the blunt front edge of the section is fully exposed to the crop entering during the entire sickle stroke cycle. This presents a barrier to crop entry for any crop directly contacting the front edge of the section. The front edge must be blunt in order to avoid too narrow a point becoming too weak and vulnerable to breakage.
The pointed guard has an advantage of presenting a point to the incoming crop so that crop is effectively divided around it. This is especially advantageous when the sickle blade is at or near the end or start of each stroke and the blunt front edge is hidden partially or entirely within the guard slot. Since the sickle bar velocity is lowest at or near the end or start of each stroke this gives the pointed guard a considerable advantage.
The guards can be formed as single elements separately mounted on the guard bar or as double or even triple elements connected together side by side for common mounting and common adjustment relative to the guard bar.
U.S. Pat. No. 3,553,948 (White) issued Jan. 12, 1970 discloses a sickle bar of this general type which has a point in front of the ledger surface. However in this arrangement the point is located wholly in front of the ledger surface with no overhanging shelf extending rearwardly from the point over the ledger surface. In its place is provided a plate which is clamped to the guard bar and extends forwardly therefrom over the ledger surface to engage into a slot at the rear of the point. This acts to hold down the knife blade as it reciprocates across the ledger surface and also provides a resistance to upward bending of the point to overcome the tendency of the point to break when engaged by an obstacle at the ground surface.
Arrangements of this type are well known and very commonly used. In some cases the arrangement is of the double sickle type where each sickle bar is essentially half the length of the cutter bar and the cutter bars reciprocate in opposite phase to minimize vibrating mass and vibrations. Usually the sickle bars are timed so that they move in opposite directions so that vibrations induced into the cutter bar assembly are minimized. This allows higher knife speeds to be achieved and therefore higher ground speeds and productivity from the mower.
Several attempts have been made to perfect the area where the inboard ends of the sickles overlap during the inboard stroke near the center of the cutter bar assembly since this has always been a problem area subject to fast wear and/or poor cutting in tough cutting conditions.
U.S. Pat. No. 3,577,716 (McCarty) issued May 4, 1971 discloses a twin sickle assembly where a single endmost blade on one sickle bar overlaps with a single endmost blade on the other sickle bar during inboard stroke at a single guard point with one blade sliding directly on top of the other. The bottom blade is inverted relative to the other blades and particularly relative to the top blade across which it slides “to provide proper shearing relationship between the opposing sections.” However, the shearing edges of the opposing blades as they move toward one another meet while at the centerline of the center guard point so that, if the cutting occurs as intended between the two blades, the crop is forced to bend around the side edges of the center guard point before being cut. Alternatively the crop may be cut as the blade enters the center guard point against the side edges of the center guard point. However, on the inboard stroke the shearing edges of both sections are spaced one section thickness from the guard ledger surface which is not desirable especially in tough cutting conditions. Further, on the outboard stroke the shearing edge of the inverted section is spaced one thickness from the guard ledger as it enters the next adjacent guard point.
U.S. Pat. No. 4,236,370 (Shaver) issued Dec. 2, 1980 discloses a twin sickle assembly where at the end of the inboard stroke at least two of the end sickle blades at the inboard end of one sickle bar overlap with at least two of the blades of the other sickle bar. One sickle bar is raised so that the overlapping blades of one slide directly on top of the other through a set of special guards, used only at the center, which have a slot which has a double height to allow passage of both blades simultaneously. At the end of the outboard stroke at least one section of one sickle bar overlaps with at least one of the other sickle bar. The upper blades on the upper knife in the overlap zone are inverted so that the cutting surfaces face upwardly to cut against upper ledger surface of the special guards. The lower sections have shearing surface facing down to cut against the lower ledger surfaces of the special center guards. The guard ledger surfaces and sickle blade shearing surfaces therefore are all properly in contact in this arrangement to provide a proper shearing action. However, careful analysis will reveal that the hold downs between the guards hold the sickle bars downwardly, so that the shearing relationship between the upper inverted sections and the upper shearing surface of the special center guards will not be held to tight tolerance especially as the guards and blades start to wear. Also with the double overlap of more than one end blade, a substantial amount of crop in the center overlap area gathers between opposing sickle sections both on inboard and outboard strokes. This means the cuffing occurs between the opposing sections as they pass each other around mid-stroke rather than against the guard ledger surfaces. The shearing surfaces between the downwardly facing blade and the upwardly facing inverted blade in this center area are two thicknesses of blade apart so that there is no proper shearing action, which is not desirable in tough cutting conditions.
U.S. Pat. No. 4,246,742 (Clark) issued Jan. 27, 1981 discloses a twin sickle bar arrangement where during the inboard stroke two end sickle blades on each sickle bar overlap with the blades of one sliding directly on top of the blades of the other and cooperate with guards which have a double height slot. On the outboard stroke one blade of one sickle bar overlaps one blade of the other. The blades on the upper sickle bar in the overlap zone have their shearing surfaces facing down to cut against the blades of the lower sickle bar. The lower blades in the overlap area have square non-bevelled edges to provide a good ledger surface for the top blades to cut against. In this arrangement some cutting occurs between the opposing blades as they pass each other around mid-stroke. However, some crop gathers between the blades and the guards and has to be cut by the blade as it enters the guard slot. The shearing surface of the top blades is spaced by the thickness of a blade from the guard upper ledger surface which is not desirable in tough cutting conditions. Furthermore the crop gathered between the bottom square edged non-bevelled blades and guards must be cut without the benefit of a sharpened bevelled edge.
U.S. Pat. No. 4,644,738 (Krambeck) issued Feb. 24, 1987 discloses a twin sickle bar arrangement where a single end sickle blade on each sickle bar overlaps during inboard stroke at a single center guard with one blade sliding directly on top of the other. This leaves the center guard open at the outboard stroke. The bottom blade is mounted with shearing edge down to provide proper shearing relationship between the blade and the guard ledger surface. An adjustable two pronged hold-down is used on top of the top blade in the center overlap area. However, the shearing edges of upper blade also face down, meaning that its shearing surface end up being one thickness below the hold-down and one thickness above the guard ledger surface on the inboard stroke. This is not desirable in tough cutting conditions.
U.S. Pat. No. 4,660,361 (Remillard) issued Apr. 28, 1987 assigned to the present assignee discloses a twin sickle bar arrangement where a single end blade from each sickle bar overlaps during the inboard stroke. Both blades have their shearing surfaces facing downwardly. A special center guard is provided with two vertically spaced, upwardly facing ledger surfaces. The sickle bars are arranged vertically apart so operate on the separate ledger surfaces at the special center guard. This arrangement provides correct shearing surface to ledger relationships between sickle blades and guards on both inboard and outboard strokes. However the provision of two vertically spaced ledger surfaces requires a large vertical spacing between the two blades and thus the two sickle bars. This interferes with the ability of the reel, which sweeps the crop past the guards, to be mounted close to and consistently relative to the cutting elements which is desirable for effective cut crop removal. Secondly there is no effective means of holding the shearing surfaces of the blades at close clearances to the guard ledger surfaces at the overlap.